The "Adobe" family does not allow redistribution. For acroread there are
eqivalent open source vesions available.

The open source versions have incomplete functionality, unfortunately.
Filling forms, for instance, is missing. Some files display incorrectly.

Sincerely, I needed commercial Reader once in a few years, and that was
filling forms feature. If there is many like me (question for next poll?)
than Reader can be downloaded.

Depends... here (Spain), our government is using acrobat forms to fill up
some taxes and documents. So it will depend on your line of work whether
adobe reader is necessary. Just an example.

But I'm wonder - we all want to support open source software, but if it
comes to the point of convencience too many say we need to have this
proprietary stuff.

Right.
Do you want to serve best those wanting pure oss, or those wanting
convenience? Is serving both possible?

It is possible. Just setup selection window similar to desktop selection and
ask user:

x complete system including few free commercial programs with different
license terms than opensource

- pure oss system

If you don't understand what is pure oss system than you probably don't need
it. Leave default.

Yes, but the problem now is not installing a pure oss system (that's
easy), but distributing a pure oss dvd or not.

My variation on the original proposal is having a pure oss dvd, plus both
an online non-oss repo and a non-oss disk (CD, perhaps). Mirrors having
problems with non oss stuff do not need to mirror those, so problem solved
for all, IMO.